hrmmm
if your clutch fluid levels are good and the slave cylinder is moving fully... then my next thought would be that your throw out bearing could be shot.... how old are the clutch, pressure plate, and bearings?
could also be a bent or otherwise damaged diaphragm springs on the pressure plate
clutch disk could be warped or broken
the throw out bearing fork could be bent or damaged
*if you can do this safely* you could try putting the car in 1st gear and keeping the clutch down... then start the car and see if it stays still or lurches forward... if it doesnt move your synchros might be shot